Hydrostatic stepless transmission

ABSTRACT

A hydrostatic stepless transmission ( 1 ) comprising axial piston type hydraulic pump ( 30 ) and hydraulic motor ( 40 ) is constructed that a pump side plunger block ( 31 ) faces to a motor side plunger block ( 41 ) through their rotary sliding surfaces ( 33  and  44 ), a plurality of communication passages are formed which communicate cylinders ( 31   a  and  41   a ) formed in the plunger blocks with each other fluidally, a separation element is interposed in the communication passages, and in each of the pump and motor side plunger blocks, the separation element divides the communication passages into that of a suction area and that of a discharge area.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the construction of a hydrostatic stepless transmission and a hydro mechanical stepless transmission constructed by combining the hydrostatic stepless transmission with a planetary gear.

BACKGROUND ART

With regard to the conventional hydrostatic stepless transmission (hereinafter, referred to as “HST”) comprising axial piston type hydraulic pump and hydraulic motor, a pump rotary shaft and a motor rotary shaft are pivotally supported their both ends by bearings provided in a housing and a high pressure oil passage plate so as to be arranged in parallel to each other. Plunger blocks are attached to the rotary shafts so as not to be rotatable and are arranged so that rotary sliding surfaces thereof face to the high pressure oil passage plate.

A valve plate is interposed between each plunger block and the high pressure oil passage plate. The valve plate is fixed to the high pressure oil passage plate.

Plungers in the plunger blocks are slid along the rotary shafts by a swash plate disposed oppositely to the high pressure oil passage plate about the plunger blocks so as to supply and discharge oil between the pump and motor (for example, see the Japanese Patent Laid Open Gazette 2003-035276).

However, with regard to the above-mentioned conventional HST, oil may leak from a relative rotary sliding surface (mating surface) between the valve plate and the plunger block. There are two relative rotary sliding surfaces at the sides of the pump and motor, therefore the volume efficiency is reduced by the oil leak and the power loss of a charge pump is increased.

With regard to the above-mentioned conventional HST, the rotary sliding surface of the plunger block fits to the valve plate, which is fixed to the high pressure oil passage plate so as not to be rotatable relatively, so as to form the relative rotary sliding surface, whereby the relative rotation speed thereof is the rotation speed of the plunger block itself. Accordingly, much power loss is occurred by the friction between the valve plate and the plunger block. Similarly to the oil leak, there are two relative rotary sliding surfaces at the sides of the pump and motor, therefore the frictional resistance influences the power loss greatly.

Furthermore, with regard to the above-mentioned conventional HST, load of radial direction is applied on the plunger block by slanting the swash plate. The load of radial direction provides rotation moment to the rotary shaft so that rotation load is applied on the bearing pivotally supporting the rotary shaft, thereby generating the power loss.

On the other hand, there is well known a hydro mechanical stepless transmission (hereinafter, referred to as “HMT”) constructed by combining the above-mentioned hydrostatic stepless transmission with a planetary gear.

With regard to the planetary gear, power is inputted into either one element of three elements, a sun gear, an internal gear and a planet carrier (first element). Output rotation is taken out from either of the two remaining elements (second element), and output or input to the HST is interlocked with the other element (third element).

The HMT is divided into two types by whether output of the HST or input to the HST is interlocked with the third element. The former is referred to as input separation type, and the latter is referred to as output separation type.

The third element is interlocked with the HST by a power transmission shaft. The power transmission shaft is interlocked with the input or output shaft of the HST through gears.

There is the above-mentioned HST that the rotary sliding surfaces of the plunger block, respectively attached to the parallel rotary shafts so as not to be rotatable relatively, touch to the high pressure oil passage plate so as to arrange the hydraulic pump and hydraulic motor in parallel to each other (this construction is referred to as the second conventional construction of the HST; see the Japanese Patent Laid Open Gazette 2000-127785).

There is also well known a HMT whose hydraulic pump and hydraulic motor are disposed coaxially. That of the input separation type has a fixed delivery hydraulic pump and variable delivery hydraulic motor. On the other hand, that of the output separation type has a variable delivery hydraulic pump and fixed delivery hydraulic motor (this construction is referred to as the third conventional construction of the HMT; see the Japanese Patent Laid Open Gazette Hei. 9-105449). With regard to the art disclosed in this patent literature, the input separation type is adopted, and a fixed swash plate of a hydraulic pump is inserted into a hollow input shaft.

However, with regard to the above-mentioned second conventional construction of the HMT, the oil leak from the HST part and the frictional loss reduce the transmission efficiency. This is because two relative rotary sliding surfaces (mating surfaces) are formed between two plunger blocks and the high pressure oil passage plate so that the oil leak at the relative rotary sliding surfaces and the frictional resistance influence the power loss greatly. Furthermore, with regard to the second conventional construction, many parts, such as the power transmission shaft, bearings, gears and the like, exist, whereby the power loss becomes large and the production cost becomes high. A plurality of shafts arranged in parallel to each other, bearings and gears prevents the downsizing of the transmission.

On the other hand, with regard to the above-mentioned third conventional construction of the HMT, the swash plate of the hydraulic pump is inserted into the hollow input shaft. Accordingly, the swash plate is rotated, whereby the hydraulic pump cannot be constructed to be variable delivery type. Therefore, speed change ratio cannot be lower than the fixed speed change ratio univocally determined by the angle of the fixed swash plate. Namely, stepless speed change from zero cannot be performed. Furthermore, forward/reverse rotation cannot be performed only by operating the swash plate, whereby a mechanism for switching forward/backward traveling is required. Similarly, with regard to the output separation type, the swash plate of the hydraulic motor is rotated, whereby the hydraulic motor cannot be constructed to be variable delivery type. Accordingly, the range of speed change cannot be wide. Furthermore, if forward/reverse rotation is performed by operating the swash plate, it is necessary to make the capacity of the hydraulic pump twice larger than that of the hydraulic motor. Thus, with regard to the third conventional construction, the range of speed change is shallow, and a mechanism for switching forward/backward traveling increases the production cost.

Considering the problems about the conventional constructions, the present invention suggests a HST of new construction and a HMT constructed by combining the HST with a planetary gear.

SUMMARY OF THE INVENTION

According to the present invention, a hydrostatic stepless transmission comprising axial piston type hydraulic pump and hydraulic motor is constructed that a pump side plunger block faces to a motor side plunger block through their rotary sliding surfaces, a plurality of communication passages are formed which communicate cylinders formed in the plunger blocks with each other fluidally, a separation element is interposed in the communication passages, and in each of the pump and motor side plunger blocks, the separation element divides the communication passages into that of a suction area and that of a discharge area.

Accordingly, one relative rotary sliding surface (mating surface) is formed. Then, compared with the conventional construction that two relative rotary sliding surfaces are formed against the high pressure oil passage plate, the leak amount from the relative rotary sliding surface is reduced relatively. Therefore, the required amount of charge oil is suppressed, thereby reducing the power loss and the cost. Both of the plunger blocks rotate in the same direction so as to rotate relatively in the rotation speed calculated as the remainder of the rotation speeds thereof, thereby reducing the power loss generated between the rotary sliding surfaces.

The separation element is constructed in each of the plunger blocks by spool valves of the same number as the cylinders of the plunger block, the spool valves are arranged slidably radially centering on a rotary shaft of the plunger block, outer ends of the spool valves touch an inner peripheral surface of an inner ring of a bearing arranged eccentrically against the rotary shaft, the spool valves are slid following rotation of the plunger block along radial direction of the rotary shaft so as to open and close the oil passages communicating the cylinders of the plunger blocks with each other, and by closing the oil passages by the spool valves, each of the plunger blocks is divided into the suction area or the discharge area.

Accordingly, the rotary shaft of the motor side plunger block and that of the pump side plunger block can be disposed coaxially, whereby the hydrostatic stepless transmission can be constructed compactly.

The rotary shaft of the pump side plunger block and the rotary shaft of the motor side plunger block are disposed coaxially, and the rotary shaft and a planetary gear are combined so as to construct an input separation type hydro mechanical stepless transmission.

Accordingly, two rotary shafts of the HST and a sun gear of the planetary gear can be disposed coaxially. Compared with the conventional construction that the third element of the planetary gear is interlocked with the HST through power transmission shafts, gears and the like, the invention can omit the power transmission shafts and gears, whereby the hydro mechanical stepless transmission can be constructed compactly with low cost.

The rotary shaft of the pump side plunger block and the rotary shaft of the motor side plunger block are disposed coaxially, and the rotary shaft and a planetary gear are combined so as to construct an output separation type hydro mechanical stepless transmission.

Accordingly, two rotary shafts of the HST and a sun gear of the planetary gear can be disposed coaxially. Compared with the conventional construction that the third element of the planetary gear is interlocked with the HST through power transmission shafts, gears and the like, the invention can omit the power transmission shafts and gears, whereby the hydro mechanical stepless transmission can be constructed compactly with low cost.

The inner peripheral surface of the inner ring of the bearing is slanted against the axis of the rotary shaft.

Accordingly, the parts of the tip parts which touch the inner peripheral surface are rotatively slid, thereby improving the durability of the tip parts of the spool valves.

The sliding direction of the spool valves is slanted against the axis of the rotary shaft.

Accordingly, the parts of the tip parts which touch the inner peripheral surface of the bearing are rotatively slid, thereby improving the durability of the tip parts of the spool valves.

The separation element is constructed that the rotary shafts arranged eccentrically support respectively the pump side plunger block and the motor side plunger block, a pump side port and a motor side port respectively communicated with the cylinders formed in the plunger blocks are formed so as to face to a relative rotary sliding surface between the plunger blocks, an oil passage is formed which communicates the ports of the plunger blocks, which are shifted by the eccentric arrangement, with each other by overlapping the ports of the plunger blocks with each other, the oil passage is closed by not overlapping the ports of the plunger blocks with each other on an extension of a line connecting the axes of the rotary shafts, and the closed oil passage of the oil passages divides the oil passages of each of the plunger blocks into that of the suction area and that of the discharge area.

Accordingly, the separation element can be constructed by the simple construction, such as the eccentric arrangement of the rotary shafts, whereby the part number of the hydrostatic stepless transmission can be reduced.

An oil passage plate rotated integrally with one of the plunger blocks is provided, and the oil passage plate touches the other plunger block slidably rotatively relatively so as to demarcate the relative rotary sliding surface between the plunger blocks, a plurality of oil passages are penetratively formed axially in the oil passage plate, an arrangement of the oil passages is substantially the same as that of the ports of the rotary sliding surface of the plunger block rotated integrally with the oil passage plate, and the rotary shaft of the plunger block rotated integrally with the oil passage plate is supported by the oil passage plate.

Accordingly, sliding resistance generated between the rotary sliding surfaces of the plunger blocks can be reduced with easy construction, whereby the power loss can be reduced. By supporting the rotary shaft by the oil passage plate, the rotary shaft is prevented from being unstable.

A charge oil supply mechanism is disposed between a connection point to the charge pump provided in a case housing of the hydrostatic stepless transmission and the hydraulic circuit in the motor or pump side plunger block.

For example, the oil passage is formed inside the fixed swash plate, the plunger block or the rotary shaft so as to make the hydrostatic stepless transmission compact.

A check valve mechanism is disposed between a connection point to the charge pump provided in a case housing of the hydrostatic stepless transmission and the hydraulic circuit in the motor or pump side plunger block.

For example, the check mechanism is provided inside the fixed swash plate, the plunger block or the rotary shaft so as to make the hydrostatic stepless transmission compact.

The case housing of the hydrostatic stepless transmission is divided near the separation element.

Accordingly, each of the case housings is respectively installed therein with the hydraulic pump or the hydraulic motor, whereby the installation becomes easy.

The case housing of the hydrostatic stepless transmission is divided, the hydraulic motor and hydraulic pump are housed in a first housing, and an opening of the first housing is closed by the other housing.

Accordingly, compared with the configuration housing the motor and pump respectively in several housings, the rigidity of the housing is higher.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view of a first embodiment of a HST.

FIG. 2 is an arrow sectional view of the line II-II in FIG. 1.

FIG. 3 is an arrow sectional view of the line III-III in FIG. 1.

FIG. 4 is a diagram of an oil passage, formed between plunger blocks, which is divided into sections.

FIG. 5 (a) is a diagram of an oil passage formed in the first section.

FIG. 5 (b) is a diagram of an oil passage formed in the second section.

FIG. 6 is a diagram of a rotary sliding surface of the pump side plunger block.

FIG. 7 is a diagram of a rotary sliding surface of the motor side plunger block.

FIG. 8 is a diagram of a rotary sliding surface of an oil passage plate.

FIG. 9 is a side view partially in section of a series of oil passages formed by the oil passage plate and the like.

FIG. 10 is a sectional side view of an embodiment in which a spool valve of the first embodiment is slanted.

FIG. 11 is a diagram of a slanted surface of a fixed swash plate.

FIG. 12 is a sectional plan view of a charge oil supply mechanism and a check and relief mechanism.

FIG. 13 is a diagram of a valve plate.

FIG. 14 is a sectional side view to which a second embodiment of a charge oil supply mechanism and a check and relief mechanism is applied.

FIG. 15 is a sectional side view to which a third embodiment of a charge oil supply mechanism and a check and relief mechanism is applied.

FIG. 16 (a) is a diagram of a case housing which is divided before a dividing element.

FIG. 16 (b) is a diagram of a case housing which is divided behind the dividing element.

FIG. 16 (c) is a diagram of a case housing that the hydraulic motor and hydraulic pump are housed in a first housing.

FIG. 17 is a diagram of a HST that the hydraulic motor and hydraulic pump are housed in the first housing.

FIG. 18 is an entire view of an input dividing type HMT.

FIG. 19 is a sectional side view of the HST part of the same construction.

FIG. 20 is a sectional side view of the spool valve which is slanted.

FIG. 21 is a sectional side view of the charge oil supply mechanism and the check and relief mechanism.

FIG. 22 is an entire view of an output dividing type HMT.

FIG. 23 is a sectional side view of the HST part of the same construction.

FIG. 24 is a sectional side view of the HST whose rotary axis is disposed eccentrically.

FIG. 25 is an arrow sectional view of the line XXV-XXV in FIG. 24.

FIG. 26 is a diagram of a rotary sliding surface of the pump side plunger block.

FIG. 27 is a diagram of a rotary sliding surface of the motor side plunger block.

FIG. 28 is a diagram of a rotary sliding surface of an oil passage plate.

FIG. 29 is a diagram of an oil passage which makes cylinders of the plunger blocks communicate with each other.

FIG. 30 is a diagram of a relative rotary sliding surface which is formed in the case that the oil passage plate is constructed integrally with the plunger block in the same construction.

BEST MODE FOR CARRYING OUT THE INVENTION

Explanation will be given on the embodiment according to the drawings.

<Construction of Hydrostatic Stepless Transmission>

As shown in FIGS. 1 and 2, a hydrostatic stepless transmission 1 (hereinafter, referred to as “HST 1”) is constructed as described below.

The HST 1 comprises an axial piston type pump 30 (hereinafter, referred to as “hydraulic pump 30”) and an axial piston type motor 40 (hereinafter, referred to as “hydraulic motor 40”). A pump side plunger block 31 and a motor side plunger block 41, which are supported respectively by rotary shafts 30 a and 40 a disposed coaxially, are disposed oppositely. The plunger block 41 (or 31) is provided therein with spool valves 50 of the same number as cylinders 41 a (or 31 a) of the plunger block slidably radiately centering on the rotary shaft 40 a (or 31 a). The outer tips of the spool valves 50 touch an inner peripheral surface 61 of an inner ring 60 a of a bearing 60 arranged eccentrically against the rotary shafts 30 a and 40 a, and slide radially following the motor side plunger block 41. The spool valves 50 open and close oil passages 6 a and 6 b which make the cylinders 31 a and 41 a of the plunger blocks 31 and 41 communicate with each other.

With regard to the HST 1 constructed as the above, the side of the rotary shaft 30 a on the axial direction of the rotary shafts 30 a and 40 a is regarded as the front side. Then, the hydraulic pump 30 is disposed at the front side and the hydraulic motor 40 is disposed at the rear side in case housings 2 a and 2 b divided into front and rear.

Explanation will be given below in detail. Bearings 30 b and 40 b are fitted respectively to the front side of the case housing 2 a and the rear side of the case housing 2 b. By these bearings 30 b and 40 b, the rotary shafts 30 a and 40 a are arranged coaxially while the rear end surface of the rotary shaft 30 a and the front end surface of the rotary shaft 40 a are disposed oppositely. The pump side plunger block 31 and the motor side plunger block 41 are supported respectively on the rotary shafts 30 a and 40 a so as not to be rotatable relatively, and their rotary sliding surfaces 34 and 44 are disposed oppositely. Accordingly, one relative rotary sliding surface (mating surface 5 c, see FIG. 1) is constructed.

In the case housing 2 a, a movable swash plate 33M is arranged between the bearing 30 b and the pump side plunger block 31, whereby the variable delivery hydraulic pump 30 is constructed that plungers 32 are slid longitudinally in the cylinders 31 a formed in the pump side plunger block 31 at regular intervals along the rotary shaft 30 a.

In the case housing 2 b, a fixed swash plate 43F is arranged between the bearing 40 b and the motor side plunger block 41, whereby the fixed delivery hydraulic motor 40 is constructed that plungers 42 are slid longitudinally in the cylinders 41 a formed in the motor side plunger block 41 at regular intervals along the rotary shaft 40 a.

A swash plate slanting shaft 33 a of the movable swash plate 33M of the hydraulic pump 30 is in parallel to a swash plate slanting shaft 43 a of the fixed swash plate 43F of the hydraulic motor 40. In FIG. 1, the swash plate slanting shafts 33 a and 43 a are perpendicular to the surface of the drawing.

As shown in FIG. 1, the sum total of the base areas 32 t of the cylinders 31 a of the pump side plunger block 31 at the side of the rotary sliding surface 34 is set to be substantially equal to the sum total of the base areas 42 t of the cylinders 41 a of the motor side plunger block 41 at the side of the rotary sliding surface 44. Accordingly, the sum total of pressured area of the cylinders 31 a of the pump side plunger block 31 is substantially equal to that of the cylinders 41 a of the motor side plunger block 41.

As shown in FIG. 1, at the position at which the end surfaces of the rotary shafts 30 a and 40 a are opposite with each other, a bearing 7 is fitted to the front end of the rotary shaft 40 a so as not to be rotatable relatively, and the rear end of the rotary shaft 30 a is inserted into the bearing 7 rotatably relatively, whereby the end surfaces of the rotary shafts 30 a and 40 a are arranged oppositely closely.

As shown in FIG. 1, the motor side plunger block 41 is supported by a bearing 160 whose outer peripheral surface is fitted to the case housing 2 b.

As shown in FIGS. 1 and 6, on the rotary sliding surface 34 of the pump side plunger block 31, pump side ports 34 a are opened so as to communicate respectively with each of the cylinders 31 a. By sliding the plungers 32, oil can passes through the pump side ports 34 a.

As shown in FIGS. 1 and 7, on the rotary sliding surface 44 of the motor side plunger block 41, every two motor side ports 44 a are opened so as to communicate respectively with each of the cylinders 41 a. By sliding the plungers 42, oil can passes through the motor side ports 44 a.

As shown in FIGS. 1, 8 and 9, between the rotary sliding surface 34 of the pump side plunger block 31 and the rotary sliding surface 44 of the motor side plunger block 41, an oil passage plate 5 is interposed. The oil passage plate 5 is bound against either of the plunger blocks 31 and 41 so as not to rotate. Communication ports 5 a, whose shape and arrangement is the same as those of the ports 34 a or 44 a of the rotary sliding surface 34 or 44 of the binding plunger block 31 or 41, are opened in the oil passage plate 5. In this embodiment, the oil passage plate 5 is bound against the motor side plunger block 41, and the arrangement of the communication ports 5 a is substantially the same as that of the motor side ports 44 a of the motor side plunger block 41 shown in FIG. 7. As shown in FIGS. 1 and 9, the rotary sliding surface 34 of the pump side plunger block 31 touches a rotary sliding surface 55 of the oil passage plate 5 by a spring 31 c so as to be oil-tight, thereby forming a series of oil passage 6.

Namely, in this embodiment, the relative rotary sliding surface (mating surface 5 c) between the plunger blocks 31 and 41 of the pump and motor is set to a touching surface between the rotary sliding surface 55 of the oil passage plate 5 and the rotary sliding surface 34 of the pump side plunger block 31.

The oil passage plate 5 is provided especially for reducing the sliding resistance generated between the rotary sliding surfaces 34 and 44 and for preventing seizure thereof. For example, these rotary sliding surfaces are covered by anti-seizing material. In addition, if any seizure occurs between the plunger blocks 31 and 41, it may alternatively be constructed so that the oil passage plate 5 is not provided and the rotary sliding surfaces 34 and 44 touch with each other directly.

As shown in FIGS. 1, 2 and 9, in the motor side plunger block 41, cylinders 51 a are radiately formed centering on the rotary shaft 40 a, between the cylinders 41 a and the ports 44 a of the rotary sliding surface 44. The columnar spool valves 50 are disposed slidably radially in the cylinders 51 a.

As shown in FIG. 2, a series of circular oil passage 54 is formed along the perimeter of the rotary shaft 40 a between the bottoms of the cylinders 51 a and the outer peripheral surface of the bearing 7 so as to communicate the cylinders 51 a with each other, thereby forming a series of oil chamber 51 b.

As shown in FIG. 2, the number of the spool valves 50 is equal to that of the cylinders 41 a and the spool valves 50 are arranged radiately centering on the rotary shaft 40 a. Tip parts 50 a thereof formed semiglobularly are projected radially outward from the motor side plunger block 41, and are arranged eccentrically against the rotary shaft 40 a and touch the inner peripheral surface 61 of the inner ring 60 a of the bearing 60 which is disposed around the outside of the motor side plunger block 41. The bearing 60 decanters from the rotary shaft 40 a along the axes of the swash plate slanting shafts 33 a and 43 a (see FIG. 1) which are in parallel to each other. As shown in FIG. 2, a straight line 4 h which connects an axis 60 d of the bearing 60 and an axis 40 d of the rotary shaft 40 a is in parallel to the swash plate slanting shafts 33 a and 43 a.

As shown in FIG. 1, the inside diameter of the inner peripheral surface 61 of the bearing 60 (the inner ring 60 a) becomes gradually smaller from the axial front of the rotary shaft 40 a to the rear thereof so that the inner peripheral surface 61 slants against the axis of the rotary shaft 40 a.

As shown in FIG. 2, each of the spool valves 50 is constructed to be columnar by disposing a small diameter part 50 d between two large diameter parts 50 b and 50 c. The outer peripheral surfaces of the large diameter parts 50 b and 50 c are fitted to the inner peripheral surfaces of the cylinder 51 a. As shown in FIG. 9, an oil passage 56 is formed between the outer peripheral surface of the small diameter part 50 d and the inner peripheral surfaces of the cylinder 51 a. The oil passage 56 constitutes a series of above-mentioned oil passage 6 which communicates the cylinders 41 a of the motor side plunger block 41 with the cylinders 31 a of the pump side plunger block 31. The oil passage 56 is closed by the large diameter part 50 c of the spool valve 50 at the position at which the rotation angle of the motor side plunger block 41 is a prescribed angle. Namely, as shown in FIGS. 2 and 3, the large diameter part 50 c of the spool valve 50 reaches the position of the port 44 a of the rotary sliding surface 44 at the positions of rotation angles 4 v and 4 w in which the phase is shifted for 90° against the straight line 4 h in parallel to the swash plate slanting shafts 33 a and 43 a. The height of the opening of the port 44 a in the radial direction centering on the rotary shaft 40 a is substantially equal to the axial length of the large diameter part 50 c so that the oil passage 56 is closed by the spool valve 50 at the rotation angles 4 v and 4 w. With regard to the construction shown in FIG. 2, the bearing 60 is decentered vertically against the rotary shaft 40 a. As shown in FIG. 1, when the spool valve 50 is at the highest position (with the rotation angle 4 v) or the lowest position (with the rotation angle 4 w), the oil passage 56 is closed as shown in FIG. 4.

As shown in FIG. 3, two sections 11 and 12, which are divided based on the position of the rotation angles 4 v and 4 w, is formed. In the first section 11, as shown in FIG. 5 (a), the small diameter part 50 d of the spool valve 50 overlaps the position of the port 44 a so that a series of oil passage 6 a comprising the oil passage 56 is opened. On the other hand, in the second section 12, as shown in FIG. 5 (b), the spool valve 50 projects to the outside and the large diameter part 50 c is disposed outer than the position of the port 44 a so that a series of oil passage 6 b formed through the oil chamber 51 b (the cylinder 51 a) is opened. Accordingly, by the spool valve 50, the oil passages 6 a and 6 b, which communicate the cylinders 31 a and 41 a of the plunger blocks 31 and 41 with each other, is opened and closed.

Accordingly, in the first section 11, the discharge area (or the suction area) is formed for the hydraulic pump 30 and the suction area (or the discharge area) is formed for the hydraulic motor 40. In the second section 12, the suction area (or the discharge area) is formed for the hydraulic pump 30 and the discharge area (or the suction area) is formed for the hydraulic motor 40. With regard to each of the hydraulic pump 30 and motor 40, the discharge area and the suction area are separated by the spool valve 50 including the oil passage 56.

The pump side plunger block and the motor side plunger block face to each other through the surfaces rotatively sliding mutually (the rotary sliding surfaces 33 and 44) so as to form a communication passage fluidly communicating the cylinders formed in the plunger blocks with each other (the oil passages 6 a and 6 b). Dividing elements (the spool valves 50, the bearing 60 and the like) are interposed in the communication passage so as to divide the communication passage into a passage communicating the suction area of one plunger block with the discharge area of the other plunger block (the oil passage 6 a) and a passage communicating the discharge area of the one plunger block with the suction area of the other plunger block (the oil passage 6 b). Namely, by the dividing elements, the oil passages in the plunger blocks 31 and 41 are divided into the suction area and discharge area (either of them is referred to as the oil passage 6 a, and the other thereof is referred to as the oil passage 6 b).

The dividing elements is constructed by the spool valves 50 of the same number as the cylinders of rather of the plunger blocks provided in said plunger block. The spool valves 50 are slidably provided radiately centering on the rotary shaft of the plunger block. The outer ends of the spool valves 50 touch the inner peripheral surface 60 a of the bearing 60 arranged eccentrically against the rotary shaft. Accordingly, the spool valves 50 are slid along the radial direction of the rotary shaft following the rotation of the plunger block so as to open and close the oil passage communicating the cylinders of the plunger blocks with each other. By the spool valves 50, the oil passage is divided so as to divide the oil passages in the plunger blocks into the discharge area and the suction area.

According to the above construction, a high pressure oil passage (or a low pressure oil passage) is formed in the first section 11 by the oil passages 6 a, and a low pressure oil passage (or a high pressure oil passage) is formed in the second section 12 by the oil passages 6 b so as to construct the HST 1 that oil is supplied from the hydraulic pump 30 to the hydraulic motor 40 with the rotary shaft 30 a as an input shaft and the rotary shaft 40 a is driven as an output shaft.

According to the above construction, as shown in FIG. 1, the swash plate slanting shaft 33 a of the movable swash plate 33M of the hydraulic pump 30 is in parallel to the swash plate slanting shaft 43 a of the fixed swash plate 43F of the hydraulic motor 40. Accordingly, by setting the slanting direction of the swash plates 33M and 43F the same in the main driving direction (for example, the forward traveling direction of the vehicle having the HST 1), the loads in the thrust direction and radial direction, based on the rotary shafts 30 a and 40 a and generated by the slide of the plungers 32 of the hydraulic pump 30 and the plungers 42 of the hydraulic motor 40, offset each other. Therefore, the motor side plunger block 41 can be supported by the smaller bearing 160, thereby reducing the power loss and the cost.

According to the above construction, as shown in FIG. 1, the sum total of pressured area of the cylinders 31 a of the pump side plunger block 31 is substantially equal to that of the cylinders 41 a of the motor side plunger block 41. Accordingly, the above-mentioned loads in the thrust direction and radial direction can offset each other more certainly. As far as the sum totals are substantially equal to each other, the number of the cylinders 31 a and 41 a is not limited, whereby the flexibility of the design of the plunger blocks is high.

According to the above construction, the rotary shaft 40 a of the motor side plunger block 41 and the rotary shaft 30 a of the pump side plunger block 31 can be disposed coaxially, whereby the hydrostatic stepless transmission 1 can be constructed compactly.

According to the above construction, as shown in FIG. 1, the pump side plunger block 31 and the motor side plunger block 41 rotate in the same direction so as to rotate relatively in the rotation speed calculated as the remainder of the rotation speeds thereof, thereby reducing the power loss generated between the rotary sliding surfaces 34 and 44 (55).

According to the above construction, as shown in FIG. 1, one relative rotary sliding surface (the mating surface 5 c) is formed by facing the rotary sliding surfaces 34 and 44 (55) to each other. Accordingly, compared with the conventional construction that two relative rotary sliding surfaces are formed against the high pressure oil passage plate, the leak amount from the relative rotary sliding surface (the mating surface 5 c) is reduced relatively. Therefore, the required amount of charge oil is suppressed, thereby reducing the power loss and the cost.

According to the above construction, as shown in FIG. 1, the high pressure oil passage plate, which is necessary in the conventional construction, is not provided, whereby the mass of the whole HST 1 can be reduced and the cost can be reduced.

According to the above construction, as shown in FIG. 1, the rotary shafts 30 a and 40 a are pivotally supported by the bearings 30 b and 40 b, and the rear end surface of the rotary shaft 30 a and the front end surface of the rotary shaft 40 a are disposed closely oppositely. Accordingly, compared with the conventional construction that bearings are disposed in the high pressure oil passage plate so as to support rotary shafts pivotally, the total length of the HST 1 can be made compact.

According to the above construction, as shown in FIG. 1, by providing the oil passage plate 5, sliding resistance generated between the rotary sliding surfaces 34 and 44 can be reduced with easy construction. Therefore, the power loss can be reduced.

According to the above construction, as shown in FIG. 1, the inner peripheral surface 61 of the inner ring 60 a of the bearing 60 slants against the axis of the rotary shaft 40 a. Accordingly, the tip parts 50 a of the spool valves 50, formed semiglobular and touching the inner peripheral surface 61, are rotated centering on the slide direction of the spool valves 50 following the rotation of the motor side plunger block 41. Therefore, the parts of the tip parts 50 a which touch the inner peripheral surface 61 are rotatively slid, thereby improving the durability of the tip parts of the spool valves 50.

Another construction for improving the durability of the spool valves 50 is shown in FIG. 10. In this case, the cylinders 51 a in which the spool valves 50 are slid is formed so as to slant against the axis of the rotary shaft 40 a in the motor side plunger block 41, whereby the slide direction of the spool valves slants against the axis of the rotary shaft 40 a. The inner peripheral surface 61 of the inner ring 60 a of the bearing 60 may be constructed flat. According to this construction, similarly to the construction that the inner peripheral surface 61 slants, the durability of the spool valves 50 is improved by rotating the spool valves 50 against the slide direction. Moreover, a general-purpose bearing whose inner peripheral surface 61 is flat can be used.

<Charge and Relief Mechanism>

Next, explanation will be given on the charge oil supply mechanism and the check and relief mechanism of the HST constructed as the above.

This construction described below shows a concrete embodiment of the construction that the charge oil supply mechanism and the check and relief mechanism are disposed between a connection point to the charge pump (a charge oil passage 2 f) provided in the case housing 2 b of the HST 1 and the hydraulic circuit in the motor or pump side plunger block. These members are provided inside the fixed swash plate, the plunger block or the rotary shaft so as to make the HST 1 compact.

With regard to the first embodiment, the charge oil supply mechanism and the check and relief mechanism are disposed in the fixed swash plate 43 f of the hydraulic motor 40.

With regard to the second embodiment, the charge oil supply mechanism and the check and relief mechanism are disposed in the motor side plunger block 41 of the hydraulic motor 40.

With regard to the third embodiment, the charge oil supply mechanism and the check and relief mechanism are disposed in the rotary shaft 40 a of the hydraulic motor 40.

Explanation will be given on each of the embodiments below.

<First Embodiment of Charge Oil Supply Mechanism and Check and Relief Mechanism>

The first embodiment of the charge oil supply mechanism and the check and relief mechanism is shown in FIGS. 1, 11 and 13.

With regard to this embodiment, as shown in FIGS. 1 and 12, shoes 46 are provided in the plungers 42 of the hydraulic motor 40. A charge oil passage 47 formed in the fixed swash plate 43F of the hydraulic motor 40 is communicated with the cylinders 41 a of the motor side plunger block 41 through communication oil passages 46 a formed in the shoes 46 and communication oil passages 42 a formed in the plungers 42. The charge oil passage 47 in the fixed swash plate 43F comprises check and relief valves 48L and 48R (see FIG. 12).

In more detail, as shown in FIGS. 11 and 12, a series of through hole 43 c, which forms the charge oil passage 47, is bored laterally in the fixed swash plate 43F. The left and right openings of the through hole 43 c is closed by the check and relief valves 48L and 48R. A charge oil passage 43 d is formed from the substantial center of the through hole 43 c to the rear portion thereof, and is communicated with the charge pump (not shown) through the charge oil passage 2 f formed in the case housing 2 b as shown in FIG. 1.

As shown in FIGS. 11 and 12, a pair of kidney ports 43L and 43R is formed in a slanted surface 43 f of the fixed swash plate 43E The kidney ports 43L and 43R are communicated with relief spring chambers 48 a of the check and relief valves 48L and 48R through communication oil passages 43 b.

As shown in FIGS. 1 and 13, a valve plate 49 is fixed to the slanted surface 43 f of the fixed swash plate 43F. Kidney ports 49 a are circumferentially formed on the valve plate 49 so as to divide it into four, whereby the kidney ports 49 a form a series of oil passage with the kidney ports 43L and 43R of the slanted surface 43 f. In addition, bridges 49 b and 49 c are formed between the kidney ports 49 a. The bridges 49 b provided in the upper and lower portions of the valve plate 49 divide the communication between the kidney ports 43L and 43R, and the bridges 49 c provided in the left and right portions of the valve plate 49 maintain the intensity of the valve plate 49. The valve plate 49 is provided especially for reducing sliding resistance between the fixed swash plate 43F and intermediate plates 146 discussed later, and for preventing seizure. These sliding surfaces are coated with, for example, anti-seizing material. In addition, if any seizure occurs between the fixed swash plate 43F and the intermediate plates 146, it may alternatively be constructed so as not to provide the valve plate 49.

As shown in FIG. 1, fixed swash plate side cylinder parts 46 b of the shoes 46 are interposed between the valve plate 49 and the shoes 46 so that the intermediate plates 146, which rotate centering on the rotary shaft 40 a integrally with the shoes 46, are pinched. Flat-bottomed insertion holes 146 b are bored in the intermediate plates 146 from the opposite side of the valve plate 49. The fixed swash plate side cylinder parts 46 b of the shoes 46 are inserted into the insertion holes 146 b so that the end surfaces of the fixed swash plate side cylinder parts 46 b touch the flat bottoms of the insertion holes 146 b. Communication oil passages 146 a, which slant when viewed in side, is formed in the intermediate plates 146 so as to communicate the kidney ports 49 a of the valve plate 49 with the communication oil passages 46 a of the shoes 46.

As shown in FIG. 1, a retainer plate 246 is slidingly held by a spherical part 41 b provided at the rear end of the plunger block 41 so as to prevent the shoes 46 from separating from the intermediate plates 146.

As shown in FIG. 1, the communication oil passages 42 a is formed along the sliding direction of the plungers 42 so as to communicate the cylinders 41 a with the communication oil passages 46 a of the shoes 46.

Then, the communication oil passages 42 a, the communication oil passages 46 a, the communication oil passages 146 a, the kidney ports 49 a and the kidney ports 43L and 43R constitute a series of communication oil passage which communicates the cylinders 41 a of the motor side plunger block 41 with the charge oil passage 47 of the fixed swash plate 43F.

According to the above construction, the cylinders 41 a of the motor side plunger block 41 are communicated with the charge oil passage 47 through the check and relief valves 48L and 48R so as to construct a charge oil supply circuit and a relief circuit of the closed hydraulic circuit (the oil passages 6 a and 6 b) formed between the hydraulic pump 30 and the hydraulic motor 40.

According to the above construction, the check and relief valves 48L and 48R as the charge oil supply mechanism and the relief mechanism are disposed inside the fixed swash plate 43F of the hydraulic motor 40. Accordingly, any space is required for providing the charge oil supply mechanism and the relief mechanism, thereby making the whole HST 1 compact. Furthermore, both of the mechanisms are superior in pressure resistance and oiltightness.

In addition, instead of the above construction, it may alternatively be constructed so that two through holes 43 c are provided and the check valve and relief valve are provided respectively to the through holes 43 c.

<Second Embodiment of Charge Oil Supply Mechanism and Check and Relief Mechanism>

The second embodiment of the charge oil supply mechanism and the check and relief mechanism is shown in FIG. 14.

With regard to this embodiment, a first circular oil passage 41 r, which is communicated with the oil passage 56 formed by the small diameter part 50 d of the spool valve 50, and a second circular oil passage 41 s, which communicates the cylinders 51 a of the spool valves 50 with each other so as to form the oil chamber 51 b, are provided in the motor side plunger block 41. Communication oil passages 40 u, 40V, 40 w and 40 x, which are communicated with the charge pump (not shown), are provided in the rotary shaft 40 a. The first and second circular oil passages 41 r and 41 s are communicated with the communication oil passages 40 u, 40V, 40 w and 40 x through two pairs of communication oil passages 41 e and 41 f formed in the motor side plunger block 41. Check valves 48 c are provided in one pair of the communication oil passages 41 e and 41 f, and relief valves are provided in the other pair of communication oil passages (not shown).

In more detail, as shown in FIG. 14, the charge oil passage 2 f formed in the case housing 2 b is communicated with the charge pump (not shown).

The charge oil passage 2 f is communicated with the communication oil passages 40 x and 40 w, formed inside the rotary shaft 40 a, through a swivel joint 23 formed in an inner peripheral surface of a shaft hole 2 u of the case housing 2 b.

The circular communication oil passage 40 u is formed between the rotary shaft 40 a and the inner peripheral surface of the motor side plunger block 41. The circular communication oil passage 40 u is communicated with the circular communication oil passage 40 w through circular communication oil passage 40 v.

The outer peripheral surface of the motor side plunger block 41 is pivotally supported by the bearing 160 so that the first circular oil passage 41 r is formed between the outer peripheral surface of the motor side plunger block 41 and an inner peripheral surface of an inner ring 160 a of the bearing 160. The first circular oil passage 41 r is communicated through a communication oil passage 41 h with the oil passage 56 formed by the small diameter part 50 d of the spool valve 50.

Between the inner peripheral surface of the motor side plunger block 41 and the outer peripheral surface of the bearing 7, the second circular oil passage 41 s is formed so as to communicate the cylinders 51 a of the spool valves 50 with each other so as to form the oil chamber 51 b.

The two pairs of the communication oil passages 41 e and 41 f are formed in the motor side plunger block 41 while being shifted the phases thereof with each other centering on the axis of the rotary shaft 40 a so as to communicate the first and second circular oil passages 41 r and 41 s with the communication oil passage 40 u. The check valves 48 c are provided in one pair of the communication oil passages 41 e and 41 f, and the relief valves are provided in the other pair of communication oil passages (not shown).

According to the above construction, the cylinders 51 a of the spool valves 50 of the motor side plunger block 41 are communicated with the charge oil passage 2 f through the check valves and relief valves so as to construct a charge oil supply circuit and a relief circuit of the closed hydraulic circuit (the oil passages 6 a and 6 b) formed between the hydraulic pump 30 and the hydraulic motor 40.

According to the above construction, the check valves 48 c and the relief valves (not shown) as the charge oil supply mechanism and the relief mechanism are disposed inside the motor side plunger block 41 of the hydraulic motor 40. Accordingly, any space is required for providing the charge oil supply mechanism and the relief mechanism, thereby making the whole HST 1 compact. Furthermore, both of the mechanisms are superior in pressure resistance and oiltightness.

Furthermore, according to the above construction, it is not necessary to provide any oil passage in the swash plate of the hydraulic motor 40. Therefore, as shown in FIG. 14, the hydraulic motor 40 can be constructed to be variable displacement type by providing the movable swash plate 43M. In addition, needless to say, it may alternatively be constructed so that the hydraulic motor 40 is constructed to be fixed displacement type by providing a fixed swash plate.

<Third Embodiment of Charge Oil Supply Mechanism and Check and Relief Mechanism>

The third embodiment of the charge oil supply mechanism and the check and relief mechanism is shown in FIG. 15.

With regard to this embodiment, a first circular oil passage 71 r, which is communicated with the oil passage 56 formed by the small diameter part 50 d of the spool valve 50, and a second circular oil passage 71 s, which communicates the cylinders 51 a of the spool valves 50 with each other so as to form the oil chamber 51 b, are provided in the motor side plunger block 41. Communication oil passages 70 w and 70 x, which are communicated with the charge pump (not shown), are provided in the rotary shaft 40 a.

The first and second circular oil passages 71 r and 71 s are communicated with the communication oil passages 70 w and 70 x through two pairs of communication oil passages 71 e and 71 f formed in the rotary shaft 40 a. A pair of check valves 78 c is provided in one pair of the communication oil passages 71 e and 71 f, and the relief valves are provided in the other pair of communication oil passages (not shown).

In more detail, as shown in FIG. 15, the charge oil passage 2 f formed in the case housing 2 b is communicated with the charge pump (not shown).

The charge oil passage 2 f is communicated with the communication oil passages 70 x and 70 w, formed inside the rotary shaft 40 a, through the swivel joint 23 formed in an inner peripheral surface of the shaft hole 2 u of the case housing 2 b.

The communication oil passage 70 w is formed axially in the rotary shaft 40 a, and the communication oil passages 71 e and 71 f are formed radiately from the communication oil passage 70 w to the inner peripheral surface of the motor side plunger block 41. In addition, two pairs of the communication oil passages 71 e and 71 f are constructed. Namely, four communication oil passages 71 e and 71 f are formed, and two communication oil passages 71 e and 71 f thereof are provided therein with the check valves 78 c, and the other two communication oil passages (not shown) are provided therein with the relief valves.

The outer peripheral surface of the motor side plunger block 41 is pivotally supported by the bearing 160 so that the first circular oil passage 71 r is formed between the outer peripheral surface of the motor side plunger block 41 and an inner peripheral surface of an inner ring 160 a of the bearing 160. The first circular oil passage 71 r is communicated through a communication oil passage 71 h with the oil passage 56 formed by the small diameter part 50 d of the spool valve 50.

Between the inner peripheral surface of the motor side plunger block 41 and the outer peripheral surface of the rotary shaft 40 a, the second circular oil passage 71 s is formed so as to communicate the cylinders 51 a of the spool valves 50 with each other so as to form the oil chamber 51 b.

Communication oil passages 71 m are formed in the motor side plunger block 41 so as to connect the first circular oil passage 71 r to the communication oil passages 71 e of the rotary shaft 40 a. As the above mentioned, two communication oil passages 71 e are formed while being shifted the phases thereof with each other centering on the axis of the rotary shaft 40 a, and two communication oil passages 71 m are also formed.

The second circular oil passage 71 s is communicated with the communication oil passages 71 f of the rotary shaft 40 a.

The check valves 78 c are provided in one pair of the communication oil passages 71 e and 71 f, and the relief valves (not shown) are provided in the other pair of communication oil passages 71 e and 71 f (not shown).

According to the above construction, the cylinders 51 a of the spool valves 50 of the motor side plunger block 41 are communicated with the charge oil passage 2 f through the check valves and relief valves so as to construct a charge oil supply circuit and a relief circuit of the closed hydraulic circuit (the oil passages 6 a and 6 b) formed between the hydraulic pump 30 and the hydraulic motor 40.

According to the above construction, the check valves 78 c and the relief valves (not shown) as the charge oil supply mechanism and the relief mechanism are disposed inside the rotary shaft 40 a. Accordingly, any space is required for providing the charge oil supply mechanism and the relief mechanism, thereby making the whole HST 1 compact. Furthermore, both of the mechanisms are superior in pressure resistance and oiltightness.

Furthermore, according to the above construction, it is not necessary to provide any oil passage in the swash plate of the hydraulic motor 40. Therefore, as shown in FIG. 15, the hydraulic motor 40 can be constructed to be variable displacement type by providing the movable swash plate 43M. In addition, needless to say, it may alternatively be constructed so that the hydraulic motor 40 is constructed to be fixed displacement type by providing a fixed swash plate.

<Construction of Case Housing>

Next, explanation will be given on the construction of the case housing of the HST 1 constructed as the above.

As shown in FIG. 16, three embodiments are suggested as the construction of the case housing.

With regard to the construction that the case housing of the HST 1 is divided at the position near the spool valve 50 as a separation element of high and low pressure of pressure oil, the first embodiment is constructed so that the case housing is divided before the spool valve 50 as the separation element.

With regard to the construction that the case housing of the HST 1 is divided at the position near the spool valve 50 as a separation element of high and low pressure of pressure oil, the second embodiment is constructed so that the case housing is divided behind the spool valve 50 as the separation element.

With regard to the third embodiment, the case housing of the HST 1 is divided so that the hydraulic motor 40 and the hydraulic pump 30 are housed in the first housing and the opening of the first housing is closed by the other housing.

Explanation will be given on each embodiment below.

<First Embodiment of Case Housing>

As shown in FIGS. 1 and 16 (a), with regard to the construction that the case housing of the HST is divided at the position near the spool valve 50 as a separation element of high and low pressure of pressure oil, the first embodiment is constructed so that the case housing is divided before the spool valve 50 as the separation element.

As shown in FIG. 1, the case housing is divided into front and rear. In the case housing 2 b in which the hydraulic motor 40 is disposed, a bearing hole 20 a, into which the bearing 60 arranged eccentrically against the rotary shaft 40 a is inserted, and a bearing hole 20 b, into which the bearing 160 of the motor side plunger block 41 is inserted, are formed.

According to this construction, for example at the processing of the case housing 2 b, the bearing hole 20 a can be processed while holding the case housing 2 b after the processing of the bearing hole 20 b. Accordingly, the design value of relation between the bearing 60 and the bearing 160 can be realized, thereby improving the processing accuracy of the decentering of the bearing 60 against the axes of the rotary shafts 30 a and 40 a.

As shown in FIGS. 1 and 14, the case housing is divided into front and rear, and a half bearing guide 21 of the movable swash plate 33M and a bearing hole 22 for the bearing 30 b of the rotary shaft 30 a as an input shaft are formed integrally with the case housing 2 a at the side of the hydraulic pump 30. On the other hand, the swivel joint 23 (only in the construction in FIG. 14, that is, the case that the second embodiment of the charge oil supply mechanism and the check and relief mechanism is adopted), a half bearing guide 27 of the movable swash plate 43M (also only in the construction in FIG. 14), the bearing hole 20 a for the bearing 60 of the spool valve 50, and a bearing hole 24 for the rotary shaft 40 a as an output shaft are formed integrally with the case housing 2 b at the side of the hydraulic motor 40.

According to this construction, the mechanical processing can be reduced by molding the case housing by die casting, thereby reducing the cost.

With regard to the above-mentioned construction, the hydraulic pump 30 is constructed to be variable displacement type, and the hydraulic motor 40 is constructed to be fixed displacement type or variable displacement type. However, the hydraulic pump 30 may alternatively be constructed to be fixed displacement type.

With regard to the above-mentioned construction, the spool valves 50 are slidably disposed in the motor side plunger block 41. However, on the contrary, the spool valves 50 may alternatively be slidably disposed in the pump side plunger block 31. In this case, the charge oil supply mechanism and the check and relief mechanism are provided in the hydraulic pump 30.

With regard to the construction (not shown) that the hydraulic pump 30 is constructed to be fixed displacement type, the hydraulic motor 40 is constructed to be fixed displacement type or variable displacement type, and the spool valve 50, the charge oil supply mechanism and the check and relief mechanism are provided in the hydraulic pump 30, the case housing is divided into front and rear, and the swivel joint 23, the bearing hole 20 a for the bearing 60 of the spool valve 50, and the bearing hole 22 for the bearing 30 b of the rotary shaft 30 a as an input shaft are formed integrally with the case housing 2 a at the side of the hydraulic pump 30. On the other hand, the half bearing guide 21 of the movable swash plate 43M and the bearing hole 24 for the bearing 30 b of the rotary shaft 40 a as an output shaft are formed integrally with the case housing 2 b at the side of the hydraulic motor 40.

Accordingly, in addition to the above-mentioned embodiment, the mechanical processing can also be reduced by molding the case housing by die casting in the construction that that the hydraulic pump 30 is constructed to be fixed displacement type and the hydraulic motor 40 is constructed to be variable displacement type, thereby reducing the cost.

<Second Embodiment of Case Housing>

As shown in FIG. 16 (b), with regard to the construction that the case housing is divided at the position near the spool valve 50 as a separation element of high and low pressure of pressure oil, the second embodiment is constructed so that the case housing is divided behind the spool valve 50 as the separation element.

In this case, shaft holes for the bearings 60 and 160 are respectively processed in the case housings 2 a and 2 b.

<Third Embodiment of Case Housing>

As shown in FIG. 16 (c), with regard to the third embodiment, the case housing of the HST 1 is divided so that the hydraulic motor 40 and the hydraulic pump 30 are housed in a first housing 222 b and the opening of the first housing 222 b is closed by the other housing (a second housing 222 a).

In this construction, the cylinder part of the first housing 222 b is constructed long, and both the hydraulic motor 40 and the hydraulic pump 30 are disposed in the cylinder part.

The bearings 60 and 160 are fitted to a step part 89 formed in the first housing 222 b. With regard to this embodiment that the hydraulic motor 40 and the hydraulic pump 30 are inserted rightward in the diagram, a retaining ring 88 is fitted so as to prevent the bearing 60 from falling out.

The second housing 222 a closes the opening of the first housing 222 b in which the hydraulic motor 40 and the hydraulic pump 30 are disposed. The half bearing guide 21 of the movable swash plate 33M of the hydraulic pump 30 is constructed in the second housing 222 a.

In this embodiment, the hydraulic motor 40 and the hydraulic pump 30 are disposed in the first housing 222 b. Accordingly, compared with the construction that the motor and pump are housed individually in several housings, the rigidity of the housing becomes higher.

In addition to the construction that the housing is divided into two housings 222 b and 222 a, the housing may alternatively be constructed so that both ends in the longer direction of the first housing 222 b are opened and the openings are closed (that is, the housing is divided into three parts).

<Hydro Mechanical Stepless Transmission>

Next, explanation will be given on a HMT (hydro mechanical stepless transmission) constructed by the above-mentioned HST.

<Input Separation Type>

A hydro mechanical stepless transmission 300 (hereinafter, referred to as “HMT 300”) shown in FIG. 18 is input separation type.

Namely, the HMT 300 is constructed by combining a hydrostatic stepless transmission 301 (hereinafter, referred to as “HST 301”) with a planetary gear 10 so as to change the output rotation in speed. As shown in FIGS. 18, 19 and 2, the motor side plunger block 41 (see FIG. 19) of the HST 301 is supported by a rotary shaft 130 a so as not to be rotatable relatively, and the pump side plunger block 31 is supported by a rotary shaft 140 a so as not to be rotatable relatively. The rotary shaft 140 a is hollow and arranged coaxially with the rotary shaft 130 a. The pump side plunger block 31 and the motor side plunger block 41 are disposed oppositely. The spool valves 50 are slidably disposed in the motor side plunger block 41 (or 31) radiately centering on the rotary shaft 130 a. The outer ends of the spool valves 50 touch the inner peripheral surface 61 of the inner ring 60 a of the bearing 60 arranged eccentrically against the rotary shaft 130 a. Accordingly, the spool valves 50 are slid along the radial direction of the rotary shaft following the rotation of the motor side plunger block 41 so as to open and close the oil passages 6 a and 6 b (see FIG. 2) communicating the cylinders 31 a and 41 a of the plunger blocks 31 and 41 with each other. Accordingly, the HMT 300 is constructed to be input separation type by the rotary shafts 130 a and 140 a and the planetary gear 10.

With regard to the HST 301 of the HMT 300 constructed as the above, the side of a hydraulic pump 330 on the axial direction of the rotary shafts 130 a and 140 a is regarded as the front side, and the side of a hydraulic motor 340 is regarded as the rear side. Then, the pump and the motor are disposed in the case housings 2 a and 2 b divided into front and rear.

Explanation will be given below in detail. Bearings 30 b and 40 b are fitted respectively to the front side of the case housing 2 a and the rear side of the case housing 2 b so that the bearings 30 b and 40 b pivotally support the rotary shafts 130 a and 140 a respectively. The hollow rotary shaft 140 a fit around the rotary shaft 130 a at the side of the hydraulic pump 330. The pump side plunger block 31 and the motor side plunger block 41 are supported respectively on the rotary shafts 30 a and 40 a so as not to be rotatable relatively, and their rotary sliding surfaces 34 and 44 are disposed oppositely.

In the case housing 2 a, the movable swash plate 33M is arranged between the bearing 30 b and the pump side plunger block 31, whereby the variable delivery hydraulic pump 330 is constructed that plungers 32 are slid longitudinally in the cylinders 31 a formed in the pump side plunger block 31 at regular intervals along the rotary shaft 140 a.

In the case housing 2 a, a movable swash plate 43M is arranged between the bearing 40 b and the motor side plunger block 41, whereby the variable delivery hydraulic motor 340 is constructed that plungers 42 are slid longitudinally in the cylinders 41 a formed in the motor side plunger block 41 at regular intervals along the rotary shaft 130 a.

A swash plate slanting shaft 33 a of the movable swash plate 33M of the hydraulic pump 330 is in parallel to a swash plate slanting shaft 43 a of the movable swash plate 43M of the hydraulic motor 340. In FIG. 19, the swash plate slanting shafts 33 a and 43 a are perpendicular to the surface of the drawing.

As shown in FIG. 19, the sum total of the base areas 32 t of the cylinders 31 a of the pump side plunger block 31 at the side of the rotary sliding surface 34 is set to be substantially equal to the sum total of the base areas 42 t of the cylinders 41 a of the motor side plunger block 41 at the side of the rotary sliding surface 44. Accordingly, the sum total of pressured area of the cylinders 31 a of the pump side plunger block 31 is substantially equal to that of the cylinders 41 a of the motor side plunger block 41.

As shown in FIG. 19, the bearing 7 is fitted to the longitudinal middle portion of the rotary shaft 130 a so as not to be rotatable relatively, and the rear end of the rotary shaft 140 a is inserted into the bearing 7 rotatably relatively.

As shown in FIG. 18, the rotary shaft 130 a is longer than the case housing 2 laterally. The front end of the rotary shaft 130 a is extended forward from the case housing 2 a and is connected to a sun gear 13 of the planetary gear 10, and the rear end thereof is extended rearward from the case housing 2 b and functions as an output shaft driving wheels, a working machine and the like (not shown).

As shown in FIG. 18, the front end of the rotary shaft 140 a is extended forward from the case housing 2 and is connected to an internal gear 14 of the planetary gear 10 and functions as an input shaft inputting power from a planet carrier 15 driven by a power source (not shown) so as to drive the hydraulic pump 330.

As shown in FIG. 19, the motor side plunger block 41 is supported by a bearing 160 whose outer peripheral surface is fitted to the case housing 2 b.

As shown in FIGS. 19 and 6, on the rotary sliding surface 34 of the pump side plunger block 31, pump side ports 34 a are opened so as to communicate respectively with each of the cylinders 31 a. By sliding the plungers 32, oil can passes through the pump side ports 34 a.

As shown in FIGS. 19 and 7, on the rotary sliding surface 44 of the motor side plunger block 41, every two motor side ports 44 a are opened so as to communicate respectively with each of the cylinders 41 a. By sliding the plungers 42, oil can passes through the motor side ports 44 a.

As shown in FIGS. 19 and 8, between the rotary sliding surface 34 of the pump side plunger block 31 and the rotary sliding surface 44 of the motor side plunger block 41, an oil passage plate 5 is interposed. The oil passage plate 5 is bound against either of the plunger blocks 31 and 41 so as not to rotate. Communication ports 5 a, whose shape and arrangement is the same as those of the ports 34 a or 44 a of the rotary sliding surface 34 or 44 of the binding plunger block 31 or 41. In this embodiment, the oil passage plate 5 is bound against the motor side plunger block 41, and the arrangement of the communication ports 5 a is substantially the same as that of the motor side ports 44 a of the motor side plunger block 41 shown in FIG. 7. As shown in FIGS. 19 and 20, the rotary sliding surface 34 of the pump side plunger block 31 touches a rotary sliding surface 55 of the oil passage plate 5 so as to be oil-tight, thereby forming a series of oil passage 6. The oil passage plate 5 is provided especially for reducing sliding resistance generated between the rotary sliding surfaces 34 and 44 and for preventing seizure thereof. For example, these rotary sliding surfaces are covered by anti-seizing material. In addition, if any seizure occurs between the plunger blocks 31 and 41, it may alternatively be constructed so that the oil passage plate 5 is not provided and the rotary sliding surfaces 34 and 44 touch with each other directly.

As shown in FIGS. 19, 20 and 2, in the motor side plunger block 41, cylinders 51 a are radiately formed centering on the rotary shafts 130 a and 140 a, between the cylinders 41 a and the ports 44 a of the rotary sliding surface 44. The columnar spool valves 50 are disposed slidably radially in the cylinders 51 a.

As shown in FIG. 2, a series of circular oil passage 54 is formed along the perimeter of the rotary shafts 130 a and 140 a between the bottoms of the cylinders 51 a and the outer peripheral surface of the bearing 7 so as to communicate the cylinders 51 a with each other, thereby forming a series of oil chamber 51 b.

As shown in FIG. 2, the number of the spool valves 50 is equal to that of the cylinders 41 a and the spool valves 50 are arranged radiately centering on the rotary shafts 130 a and 140 a. Tip parts 50 a thereof formed semiglobular are projected radially outward from the motor side plunger block 41, and are arranged eccentrically against the rotary shaft 130 a and touch the inner peripheral surface 61 of the inner ring 60 a of the bearing 60 which is disposed around the outside of the motor side plunger block 41. The bearing 60 decenters from the rotary shaft 130 a along the axes of the swash plate slanting shafts 33 a and 43 a (see FIG. 19) which are in parallel to each other. As shown in FIG. 2, a straight line 4 h which connects an axis 60 d of the bearing 60 and an axis 130 d of the rotary shaft 130 a is in parallel to the swash plate slanting shafts 33 a and 43 a.

As shown in FIG. 19, the inside diameter of the inner peripheral surface 61 of the bearing 60 (the inner ring 60 a) becomes gradually smaller from the axial front of the rotary shaft 130 a to the rear thereof so that the inner peripheral surface 61 slants against the axis of the rotary shaft 130 a.

As shown in FIG. 2, each of the spool valves 50 is constructed to be columnar by disposing a small diameter part 50 d between two large diameter parts 50 b and 50 c. The outer peripheral surfaces of the large diameter parts 50 b and 50 c are fitted to the inner peripheral surfaces of the cylinder 51 a. As shown in FIG. 20, an oil passage 56 is formed between the outer peripheral surface of the small diameter part 50 d and the inner peripheral surfaces of the cylinder 51 a. The oil passage 56 constitutes a series of above-mentioned oil passage 6 which communicates the cylinders 41 a of the motor side plunger block 41 with the cylinders 31 a of the pump side plunger block 31. The oil passage 56 is closed by the large diameter part 50 c of the spool valve 50 at the position at which the rotation angle of the motor side plunger block 41 is a prescribed angle. Namely, as shown in FIGS. 2 and 3, the large diameter part 50 c of the spool valve 50 reaches the position of the port 44 a of the rotary sliding surface 44 at the positions of rotation angles 4 v and 4 w in which the phase is shifted for 90° against the straight line 4 h in parallel to the swash plate slanting shafts 33 a and 43 a. The height of the opening of the port 44 a in the radial direction centering on the rotary shaft 130 a is substantially equal to the axial length of the large diameter part 50 c so that the oil passage 56 is closed by the spool valve 50 at the rotation angles 4 v and 4 w. With regard to the construction shown in FIG. 2, the bearing 60 is decentered vertically against the rotary shaft 130 a. As shown in FIG. 19, when the spool valve 50 is at the highest position (with the rotation angle 4 v) or the lowest position (with the rotation angle 4 w), the oil passage 56 is closed as shown in FIG. 4.

As shown in FIG. 3, two sections 11 and 12, which are divided based on the position of the rotation angles 4 v and 4 w, is formed. In the first section 11, as shown in FIG. 5 (a), the small diameter part 50 d of the spool valve 50 overlaps the position of the port 44 a so that a series of oil passage 6 a comprising the oil passage 56 is opened. On the other hand, in the second section 12, as shown in FIG. 5 (b), the spool valve 50 projects to the outside and the large diameter part 50 c is disposed outer than the position of the port 44 a so that a series of oil passage 6 b formed through the oil chamber 51 b (the cylinder 51 a) is opened. Accordingly, by the spool valve 50, the oil passages 6 a and 6 b, which communicate the cylinders 31 a and 41 a of the plunger blocks 31 and 41 with each other, is opened and closed.

According to the above construction, a high pressure oil passage (or a low pressure oil passage) is formed in the first section 11 by the oil passages 6 a, and a low pressure oil passage (or a high pressure oil passage) is formed in the second section 12 by the oil passages 6 b as shown in FIG. 19 so as to construct the HST 301 that oil is supplied from the hydraulic pump 330 to the hydraulic motor 340 with the rotary shaft 140 a as an input shaft and the rotary shaft 130 a is driven as an output shaft.

Then, the HST 301 constructed as the above and the planetary gear 10 are combined so as to construct the input separation type HMT 300 shown in FIG. 18.

Namely, the rotary shaft 130 a is longer than the case housing 2 laterally. The front end of the rotary shaft 130 a is extended forward from the case housing 2 a and is connected to the sun gear 13 of the planetary gear 10, and the rear end thereof is extended rearward from the case housing 2 b and functions as an output shaft driving wheels, a working machine and the like (not shown). ON the other hand, the front end of the rotary shaft 140 a is extended forward from the case housing 2 a and is connected to an internal gear 14 of the planetary gear 10 and functions as an input shaft inputting power from the planet carrier 15 driven by a power source (not shown) so as to drive the hydraulic pump 330. Furthermore, the rotary shaft 140 a is hollow and arranged coaxially with the rotary shaft 130 a.

According to the above construction, as shown in FIG. 19, the swash plate slanting shaft 33 a of the movable swash plate 33M of the hydraulic pump 330 is in parallel to the swash plate slanting shaft 43 a of the movable swash plate 43M of the hydraulic motor 340. Accordingly, by setting the slanting direction of the swash plates 33M and 43M the same in the main driving direction (for example, the forward traveling direction of the vehicle having the HMT 300), the loads in the thrust direction and radial direction, based on the rotary shafts 130 a and 140 a and generated by the slide of the plungers 32 of the hydraulic pump 330 and the plungers 42 of the hydraulic motor 340, offset each other. Therefore, the motor side plunger block 41 can be supported by the smaller bearing 160, thereby reducing the power loss and the cost.

According to the above construction, as shown in FIG. 19, the sum total of pressured area of the cylinders 31 a of the pump side plunger block 31 is substantially equal to that of the cylinders 41 a of the motor side plunger block 41. Accordingly, the above-mentioned loads in the thrust direction and radial direction can offset each other more certainly. As far as the sum totals are substantially equal to each other, the number of the cylinders 31 a and 41 a is not limited, whereby the flexibility of the design of the plunger blocks is high.

According to the above construction, as shown in FIG. 19, the pump side plunger block 31 and the motor side plunger block 41 rotate in the same direction so as to rotate relatively in the rotation speed calculated as the remainder of the rotation speeds thereof, thereby reducing the power loss generated between the rotary sliding surfaces 34 and 44 (55).

According to the above construction, as shown in FIG. 19, one relative rotary sliding surface (the mating surface 5 c) is formed by facing the rotary sliding surfaces 34 and 44 (55) to each other. Accordingly, compared with the conventional construction that two relative rotary sliding surfaces are formed against the high pressure oil passage plate, the leak amount from the relative rotary sliding surface is reduced relatively. Therefore, the required amount of charge oil is suppressed, thereby reducing the power loss and the cost.

According to the above construction, as shown in FIG. 19, the high pressure oil passage plate, which is necessary in the conventional construction, is not provided, whereby the mass of the whole HST 301 can be reduced and the cost can be reduced.

The rotary shaft 140 a of the motor side plunger block 41 is arranged coaxially with the rotary shaft 130 a of the pump side plunger block 31, and the rotary shaft 130 a is connected to the sun gear 13 of the planetary gear 310. Accordingly, the rotary shaft 130 a and 140 a and the planetary gear 310 are combined so as to construct the input separation type hydro mechanical stepless transmission 300. Therefore, the two rotary shaft 130 a and 140 a of the HST are arranged coaxially with the sun gear 13 of the planetary gear 310. Then, compared with the conventional construction that the third element of the planetary gear is interlocked with the HST through power transmission shafts and gears, thereby constructing a compact hydro mechanical stepless transmission with low cost.

According to the above construction, as shown in FIG. 19, by providing the oil passage plate 5, sliding resistance generated between the rotary sliding surfaces 34 and 44 can be reduced with easy construction. Therefore, the power loss can be reduced.

According to the above construction, as shown in FIG. 19, the inner peripheral surface 61 of the inner ring 60 a of the bearing 60 slants against the axis of the rotary shaft 130 a. Accordingly, the tip parts 50 a of the spool valves 50, formed semiglobularly and touching the inner peripheral surface 61, are rotated centering on the slide direction of the spool valves 50 following the rotation of the motor side plunger block 41. Therefore, the parts of the tip parts 50 a which touch the inner peripheral surface 61 are rotatively slid, thereby improving the durability of the tip parts of the spool valves 50.

Another construction for improving the durability of the spool valves 50 is shown in FIG. 20. In this case, the cylinders 51 a in which the spool valves 50 are slid is formed so as to slant against the axis of the rotary shaft 130 a in the motor side plunger block 41, whereby the slide direction of the spool valves slants against the axis of the rotary shaft 130 a. The inner peripheral surface 61 of the inner ring 60 a of the bearing 60 may be constructed flat. According to this construction, similarly to the construction that the inner peripheral surface 61 slants, the durability of the spool valves 50 is improved by rotating the spool valves 50 against the slide direction. Moreover, a general-purpose bearing whose inner peripheral surface 61 is flat can be used.

Compared with the above-mentioned first conventional construction, the input separation type HMT 300 constructed as the above does not require any power transmission shaft and requires less bearings and gears, whereby the power loss can be reduced. Furthermore, following the reduction of part number, the production cost can also be reduced.

With regard to the input separation type HMT 300 constructed as the above, the rotary shaft 140 a is arranged coaxially with the rotary shaft 130 a. Accordingly, compared with the above-mentioned first conventional construction, the transmission can be made compact.

With regard to the input separation type HMT 300 constructed as the above, the hydraulic pump 330 is variable delivery type so as to enable stepless speed change from zero. Accordingly, compared with the above-mentioned second conventional construction, the range of speed change becomes wider. In addition, especially in the case that there is no necessity to keep the range of speed change wide, it may alternatively be constructed so that the hydraulic pump 330 is fixed delivery type and the hydraulic motor 340 is variable delivery type.

With regard to the input separation type HMT 300 constructed as the above, the hydraulic pump 330 is variable delivery type. Accordingly, compared with the above-mentioned second conventional construction, any mechanism for switching forward/backward traveling is not required, whereby the production cost for such a mechanism can be reduced.

<Charge Oil Supply Mechanism and the Check and Relief Mechanism>

Next, explanation will be given on the charge oil supply mechanism and the check and relief mechanism of the HST 301 constructed as the above.

In addition, the above-mentioned second embodiment of the charge oil supply mechanism and the check and relief mechanism is applied to this construction. However, the first or third embodiment may alternatively be applied.

As shown in FIG. 21, the first circular oil passage 41 r, which is communicated with the oil passage 56 formed by the small diameter part 50 d of the spool valve 50, and the second circular oil passage 41 s, which communicates the cylinders 51 a of the spool valves 50 with each other so as to form the oil chamber 51 b, are provided in the motor side plunger block 41. The communication oil passages 40 u, 40 v, 40 w and 40 x, which are communicated with the charge pump (not shown), are provided in the rotary shaft 130 a. The first and second circular oil passages 41 r and 41 s are communicated with the communication oil passages 40 u, 40 v, 40 w and 40 x through two pairs of communication oil passages 41 e and 41 f formed in the motor side plunger block 41. The check valves 48 c are provided in one pair of the communication oil passages 41 e and 41 f, and relief valves are provided in the other pair of communication oil passages (not shown).

In more detail, as shown in FIG. 21, the charge oil passage 2 f formed in the case housing 2 b is communicated with the charge pump (not shown).

The charge oil passage 2 f is communicated with the communication oil passages 40 x and 40 w, formed inside the rotary shaft 130 a, through the swivel joint 23 formed in an inner peripheral surface of the shaft hole 2 u of the case housing 2 b.

The circular communication oil passage 40 u is formed between the rotary shaft 130 a and the inner peripheral surface of the motor side plunger block 41. The circular communication oil passage 40 u is communicated with the circular communication oil passage 40 w through circular communication oil passage 40 v.

The outer peripheral surface of the motor side plunger block 41 is pivotally supported by the bearing 160 so that the first circular oil passage 41 r is formed between the outer peripheral surface of the motor side plunger block 41 and an inner peripheral surface of an inner ring 160 a of the bearing 160. The first circular oil passage 41 r is communicated through a communication oil passage 41 h with the oil passage 56 formed by the small diameter part 50 d of the spool valve 50.

Between the inner peripheral surface of the motor side plunger block 41 and the outer peripheral surface of the bearing 7, the second circular oil passage 41 s is formed so as to communicate the cylinders 51 a of the spool valves 50 with each other so as to form the oil chamber 51 b.

The two pairs of the communication oil passages 41 e and 41 f are formed in the motor side plunger block 41 while being shifted the phases thereof with each other centering on the axis of the rotary shaft 130 a so as to communicate the first and second circular oil passages 41 r and 41 s with the communication oil passage 40 u. The check valves 48 c are provided in one pair of the communication oil passages 41 e and 41 f, and the relief valves are provided in the other pair of communication oil passages (not shown).

According to the above construction, the cylinders 51 a of the spool valves 50 of the motor side plunger block 41 are communicated with the charge oil passage 2 f through the check valves and relief valves so as to construct a charge oil supply circuit and a relief circuit of the closed hydraulic circuit (the oil passages 6 a and 6 b) formed between the hydraulic pump 330 and the hydraulic motor 340.

According to the above construction, the check valves 48 c and the relief valves (not shown) as the charge oil supply mechanism and the relief mechanism are disposed inside the motor side plunger block 41 of the hydraulic motor 340. Accordingly, any space is required for providing the charge oil supply mechanism and the relief mechanism, thereby making the whole HST 301 compact. Furthermore, both of the mechanisms are superior in pressure resistance and oiltightness.

With regard to the above-mentioned construction, the spool valves 50 are slidably disposed in the motor side plunger block 41. However, on the contrary, the spool valves 50 may alternatively be slidably disposed in the pump side plunger block 31. In this case, the charge oil supply mechanism and the check and relief mechanism are provided in the hydraulic pump 330.

Next, explanation will be given on the case housings 2 a and 2 b of the HST 301.

As shown in FIG. 19, the case housing is divided into front and rear. In the case housing 2 b in which the hydraulic motor 340 is disposed, the bearing hole 20 a, into which the bearing 60 arranged eccentrically against the rotary shaft 130 a is inserted, and the bearing hole 20 b, into which the bearing 160 of the motor side plunger block 41 is inserted, are formed.

According to this construction, for example at the processing of the case housing 2 b, the bearing 60 can be processed while holding the case housing 2 b after the processing of the bearing 160. Accordingly, the design value of relation between the bearing 60 and the bearing 160 can be realized, thereby improving the processing accuracy of the decentering of the bearing 60 against the axes of the rotary shafts 130 a and 140 a.

As shown in FIG. 19, the case housing is divided into front and rear, and the half bearing guide 21 of the movable swash plate 33M and the bearing hole 22 for the bearing 30 b of the rotary shaft 130 a as an input shaft are formed integrally with the case housing 2 a at the side of the hydraulic pump 330. On the other hand, the swivel joint 23, the half bearing guide 27 of the movable swash plate 43M, the bearing hole 20 a for the bearing 60 of the spool valve 50, and the bearing hole 24 for the rotary shaft 140 a as an output shaft are formed integrally with the case housing 2 b at the side of the hydraulic motor 340.

According to this construction, the mechanical processing can be reduced by molding the case housing 2 by die casting, thereby reducing the cost.

In addition, either of the constructions of the case housing shown in FIG. 16 (a) to (c) may be applied.

<Output Separation Type>

A hydro mechanical stepless transmission 320 (hereinafter, referred to as “HMT 320”) shown in FIGS. 22 and 23 is output separation type.

Namely, the HMT 320 is constructed by combining a HST 311 with a planetary gear 310 so as to change the output rotation in speed. In the HST 311, the pump side plunger block 31 is supported by a rotary shaft 130 a so as not to be rotatable relatively, and the motor side plunger block 41 is supported by a rotary shaft 140 a so as not to be rotatable relatively. The rotary shaft 140 a is hollow and arranged coaxially with the rotary shaft 130 a. The pump side plunger block 31 and the motor side plunger block 41 are disposed oppositely. The spool valves 50 are slidably disposed in the motor side plunger block 41 (or 31) radiately centering on the rotary shaft 130 a. The outer ends of the spool valves 50 touch the inner peripheral surface 61 of the inner ring 60 a of the bearing 60 arranged eccentrically against the rotary shaft 130 a. Accordingly, the spool valves 50 are slid along the radial direction of the rotary shaft following the rotation of the motor side plunger block 41 so as to open and close the oil passages 6 a and 6 b communicating the cylinders 31 a and 41 a of the plunger blocks 31 and 41 with each other. Accordingly, the HMT 300 is constructed to be output separation type by the rotary shafts 130 a and 140 a and the planetary gear 310.

The members in FIGS. 22 and 23 having the same numerals as the members of the above-mentioned input separation type HMT 300 have the same construction and function, therefore explanation thereof is omitted.

With regard to the above-mentioned output separation type HMT 320 constructed as the above, the rotary shaft 130 a is longer than the case housing 2 laterally. The front end of the rotary shaft 130 a is extended forward from the case housing 2 a and is driven by a power source (not shown) so as to function driving the hydraulic pump 330, and the rear end thereof is extended rearward from the case housing 2 b and is connected to the sun gear 13 of the planetary gear 310. ON the other hand, the rear end of the rotary shaft 140 a is extended rearward from the case housing 2 b and is connected to an internal gear 14 of the planetary gear 310. Furthermore, the rotary shaft 140 a is hollow and arranged coaxially with the rotary shaft 130 a.

The rotary shaft 140 a of the motor side plunger block 41 is arranged coaxially with the rotary shaft 130 a of the pump side plunger block 31, and the rotary shaft 130 a is connected to the sun gear 13 of the planetary gear 310. Accordingly, the rotary shaft 130 a and 140 a and the planetary gear 310 are combined so as to construct the output separation type hydro mechanical stepless transmission 320. According to the coaxial arrangement of the rotary shafts 130 a and 140 a, the hydro mechanical stepless transmission can be made compact.

The output separation type HMT 320 constructed as the above has the same effect as the above-mentioned HMT 300.

In addition, especially in the case that there is no necessity to keep the range of speed change wide, it may alternatively be constructed so that the hydraulic pump 330 is fixed delivery type and the hydraulic motor 340 is variable delivery type, or that that the hydraulic pump 330 is variable delivery type and the hydraulic motor 340 is fixed delivery type.

<Hydrostatic Stepless Transmission>

Next, explanation will be given on a hydrostatic stepless transmission whose suction area and discharge area of the opposite hydraulic pump 30 and motor 40 are constructed by decentering the rotary shafts of the pump 30 and motor 40.

As shown in FIGS. 24 and 25, a hydrostatic stepless transmission 401 (hereinafter, referred to as “HST 401”) is constructed as follows.

The HST 401 comprises an axial piston type pump 430 (hereinafter, referred to as “hydraulic pump 430”) and an axial piston type motor 440 (hereinafter, referred to as “hydraulic motor 440”). A pump side plunger block 431 and a motor side plunger block 441, which are supported respectively by rotary shafts 470 a and 480 a disposed eccentrically, are disposed oppositely. Pump side ports 434 a and motor side ports 444 a are formed in rotary sliding surfaces 434 and 444 of the plunger blocks 431 and 441 and are communicated respectively with cylinders 431 a and 441 a formed in the plunger blocks 431 and 441. When viewed radially centering on the axis of the rotary shaft 470 a, from the pump side ports 434 a at two opposite positions on a straight line which connects the axes of the rotary shafts 470 a and 480 a, the motor side ports 444 a on the same line and corresponding to the ports 434 a respectively are separated so as to be most distant (at the most eccentric positions). Compared with the motor side ports 444 a on this line, the port 444 a not on the line is less eccentric radially against the corresponding pump side ports 434 a (the amount of eccentricity thereof becomes smaller). Accordingly, the motor side port 444 a overlaps the corresponding pump side ports 434 a so that the ports 434 a and 444 a are communicated. Namely, oil passage 408 communicating the cylinders 431 a and 441 a of the plunger blocks 431 and 441 with each other is closed when the motor side cylinder 441 a reaches the most eccentric position of the motor side plunger block 441 against the pump side plunger block 431, and is opened when the cylinder 441 a is not at the position.

With regard to the HST 401 constructed as the above, the side of the rotary shaft 470 a on the axial direction of the rotary shafts 470 a and 480 a is regarded as the front side. Then, the hydraulic pump 430 is disposed at the front side and the hydraulic motor 440 is disposed at the rear side in case housings 402 a and 402 b divided into front and rear.

With regard to the above-mentioned separation element, the pump side plunger block 431 and the motor side plunger block 441 are respectively supported by the rotary shafts 470 a and 480 a arranged eccentrically. The pump side ports 434 a and motor side ports 444 a respectively communicated with the cylinders formed in the plunger blocks 431 and 441 are formed in the rotary sliding surfaces 434 and 444 of the plunger blocks 431 and 441 so as to face to the relative rotary sliding surface between the plunger blocks 431 and 441. When the ports 434 a and 444 a of the plunger blocks 431 and 441, deviating with each other in position, overlap by the eccentric arrangement of the rotary shafts 470 a and 480 a, the oil passages 408 are formed so as to communicate the cylinders of the plunger blocks with each other. On an extension of a line connecting the axes of the rotary shafts 470 a and 480 a to each other, the ports of the plunger blocks do not overlap so as to close the oil passages 408. The oil passages of each of the plunger blocks are classified into the suction area and the discharge area by whether of the oil passages 408 is closed.

Explanation will be given below in detail. Bearings 430 b and 40 b are fitted respectively to the front side of the case housing 402 a and the rear side of the case housing 402 b. By these bearings 430 b and 40 b, the rotary shafts 470 a and 480 a are arranged coaxially while the rear end surface of the rotary shaft 470 a and the front end surface of the rotary shaft 480 a are disposed oppositely. The pump side plunger block 431 and the motor side plunger block 441 are supported respectively on the rotary shafts 470 a and 480 a so as not to be rotatable relatively, and their rotary sliding surfaces 434 and 444 are disposed oppositely.

In the case housing 402 a, a movable swash plate 433M is arranged between the bearing 430 b and the pump side plunger block 431, whereby the variable delivery hydraulic pump 430 is constructed that plungers 432 are slid longitudinally in the cylinders 431 a formed in the pump side plunger block 431 at regular intervals along the rotary shaft 470 a.

In the case housing 402 b, a fixed swash plate 43F is arranged between the bearing 440 b and the motor side plunger block 441, whereby the fixed delivery hydraulic motor 440 is constructed that plungers 442 are slid longitudinally in the cylinders 441 a formed in the motor side plunger block 441 at regular intervals along the rotary shaft 480 a.

A swash plate slanting shaft 433 a of the movable swash plate 433M of the hydraulic pump 430 is in parallel to a swash plate slanting shaft 443 a of the fixed swash plate 43F of the hydraulic motor 440. In FIG. 24, the swash plate slanting shafts 433 a and 443 a are perpendicular to the surface of the drawing.

As shown in FIG. 24, the sum total of the base areas 432 t of the cylinders 431 a of the pump side plunger block 431 at the side of the rotary sliding surface 434 is set to be substantially equal to the sum total of the base areas 442 t of the cylinders 441 a of the motor side plunger block 441 at the side of the rotary sliding surface 444. Accordingly, the sum total of pressured area of the cylinders 431 a of the pump side plunger block 431 is substantially equal to that of the cylinders 441 a of the motor side plunger block 441.

As shown in FIG. 24, the motor side plunger block 441 is supported by a bearing 496 whose outer peripheral surface is fitted to the case housing 402 b. A bearing 407 is pinched between the motor side plunger block 441 and the rotary shaft 480 a so that the front end of the rotary shaft 480 a is supported by the bearing 496 through the bearing 407 and the motor side plunger block 441.

As shown in FIG. 24, the rear end surface of the rotary shaft 470 a and the front end surface of the rotary shaft 480 a are arranged oppositely closely.

As shown in FIGS. 25 and 26, on the rotary sliding surface 434 of the pump side plunger block 431, pump side ports 434 a are opened so as to communicate respectively with each of the cylinders 431 a. By sliding the plungers 432, oil can passes through the pump side ports 434 a.

As shown in FIGS. 26 and 27, on the rotary sliding surface 444 of the motor side plunger block 441, every two motor side ports 444 a are opened so as to communicate respectively with each of the cylinders 441 a. By sliding the plungers 442, oil can passes through the motor side ports 444 a.

As shown in FIGS. 24 and 27, an oil passage plate 490 is interposed between the rotary sliding surfaces 433 and 434 of the plunger blocks 431 and 441. A plurality of oil passages 490 a are penetratively formed axially in the oil passage plate 490. The arrangement of the oil passages 490 a is substantially the same as that of either of the ports 434 a and 444 a of the rotary sliding surfaces 433 and 434 of the plunger blocks 431 and 441. In this embodiment, the oil passages 490 a, whose sectional shape and arrangement are the same as the pump side ports 434 a formed in the rotary sliding surface 433 of the pump side plunger block 431, is provided in the oil passage plate 490.

The oil passage plate 490 touches the other plunger block (in this embodiment, the motor side plunger block 441) slidably rotatively relatively so as to demarcate the relative rotary sliding surface (mating surface 5 c) between the plunger blocks 433 and 444.

The oil passage plate 490 is discal and coaxially arranged on the rotary shaft 470 a supporting the plunger block on which the ports of the same arrangement as the oil passages 490 a (in this embodiment, the pump side plunger block 431).

The oil passage plate 490 is inserted into a bearing 497 arranged coaxially with the rotary shaft 470 a so as to be rotatable relatively against the pump side plunger block 431, the motor side plunger block 441 and the rotary shafts 470 a and 480 a. In addition, the oil passage plate 490 may alternatively not be rotatable relatively against the rotary shaft 470 a at the angle at which the positions of the oil passages 490 a and the pump side ports 434 a are in agreement with each other. The oil passage plate 490 may alternatively be constructed so as not to be rotatable relatively against the pump side plunger block 431 by a stopper member such as a pin and so as to be rotated integrally with the pump side plunger block 431. Namely, the oil passage plate 490, which is rotated integrally with either of the plunger blocks, is interposed between the rotary sliding surfaces of the plunger blocks. A plurality of oil passages 490 a are penetratively formed axially in the oil passage plate 490. The arrangement of the oil passages 490 a is substantially the same as that of the ports of the rotary sliding surface of the plunger block rotated integrally with the oil passage plate 490.

The rotary shaft 470 a of the pump side plunger block 431, rotated integrally with the oil passage plate 490, is supported by the oil passage plate 490, that is, the rotary shaft 470 a is supported through the oil passage plate 490 by the bearing 497. Accordingly, the rotary shaft 470 a is prevented from being unstable.

As shown in FIGS. 24 and 29, the rotary sliding surface 434 of the pump side plunger block 431 and the rotary sliding surface 444 of the motor side plunger block 441 touch rotary sliding surfaces 494 a and 494 b of the oil passage plate 490 so as to form a series of oil passage 408. In addition to supporting the shaft 470 a, the oil passage plate 490 reduces sliding resistance generated between the rotary sliding surfaces 434 and 444 and prevents seizure therebetween. Therefore, the sliding surfaces are covered by anti-seizing material. In addition, if any seizure occurs between the rotary sliding surfaces 434 and 444 and the oil passage plate 490, the covering by the anti-seizing material may be omitted.

As shown in FIGS. 24 and 25, swash plate slanting shaft 433 a of the movable swash plate 433M of the hydraulic pump 430 is in parallel to a swash plate slanting shaft 443 a of the fixed swash plate 43F of the hydraulic motor 440. The centers of the rotary shafts 470 a and 480 a are arranged eccentrically on the direction perpendicular to the swash plate slanting shafts 433 a and 443 a.

At the rotation angle at which the amount of eccentricity 499 of the rotary shafts 470 a and 480 a becomes the maximum, that is, at rotation angles 404 t and 404 u at which the phases of the shafts are shifted for 90° against the axial direction of the swash plate slanting shafts 433 a and 443 a, the shift amount between the ports 434 a (490 a) and 444 a of the rotary sliding surfaces 434 and 444 of the plunger blocks 431 and 441 becomes the maximum so that the oil passages 408 formed by overlapping the ports 434 a (490 a) and 444 a with each other are closed, and at the other rotation angle, the amount of eccentricity 499 makes the oil passages 408 communicated with each other.

Accordingly, as shown in FIG. 25, two sections 411 and 412, which are divided based on the above-mentioned position of rotation angles 404 t and 404 u, are formed. In each of the sections 411 and 412, the oil passages 408 are formed by overlapping the ports 434 a (490 a) and 444 a with each other as shown in FIG. 29.

According to the above construction, as shown in FIG. 25, a high pressure oil passage (or a low pressure oil passage) is formed in the first section 411 by the oil passages 408, and a low pressure oil passage (or a high pressure oil passage) is formed in the second section 412 by the oil passages 408 so as to construct the HST 401 that oil is supplied from the hydraulic pump 430 to the hydraulic motor 440 with the rotary shaft 470 a as an input shaft and the rotary shaft 480 a is driven as an output shaft.

In the first section 411, the discharge area (or the suction area) is formed for the hydraulic pump 430 and the suction area (or the discharge area) is formed for the hydraulic motor 440. In the second section 412, the suction area (or the discharge area) is formed for the hydraulic pump 430 and the discharge area (or the suction area) is formed for the hydraulic motor 440. The discharge area and the suction area are constructed by the eccentric arrangement of the rotary shafts 470 a and 480 a.

As the above mentioned, the pump side plunger block 431 and the motor side plunger block 441 face to each other through the surfaces rotatively sliding with each other (the rotary sliding surfaces 433 and 444) so as to form communication passages fluidly communicating the cylinders formed in the plunger blocks with each other (the oil passages 408). Dividing elements are interposed in the communication passage so as to divide the communication passages into the passage of the suction area (the first section 411 (the second section 412)) and that of the discharge area (the second section 412 (the first section 411)). Namely, by the dividing elements, the oil passages in the plunger blocks 431 and 441 are divided into the suction area and discharge area (either of them is referred to as the first section 411, and the other thereof is referred to as the second section 412).

According to the above construction, as shown in FIG. 24, the swash plate slanting shaft 433 a of the movable swash plate 433M of the hydraulic pump 430 is in parallel to the swash plate slanting shaft 443 a of the fixed swash plate 43F of the hydraulic motor 440. Accordingly, by setting the slanting direction of the swash plates 433M and 43F the same in the main driving direction (for example, the forward traveling direction of the vehicle having the HST 401), the loads in the thrust direction and radial direction, based on the rotary shafts 470 a and 480 a and generated by the slide of the plungers 432 of the hydraulic pump 430 and the plungers 442 of the hydraulic motor 440, offset each other. Therefore, the motor side plunger block 441 can be supported by the smaller bearing 496, thereby reducing the power loss and the cost.

According to the above construction, as shown in FIG. 24, the sum total of pressured area of the cylinders 431 a of the pump side plunger block 431 is substantially equal to that of the cylinders 441 a of the motor side plunger block 441. Accordingly, the above-mentioned loads in the thrust direction and radial direction can offset each other more certainly. As far as the sum totals are substantially equal to each other, the number of the cylinders 431 a and 441 a is not limited, whereby the flexibility of the design of the plunger blocks is high.

According to the above construction, as shown in FIG. 24, the pump side plunger block 431 and the motor side plunger block 441 rotate in the same direction so as to rotate relatively in the rotation speed calculated as the remainder of the rotation speeds thereof, thereby reducing the power loss generated between the rotary sliding surfaces 434 and 444 (494 a and 494 b).

According to the above construction, as shown in FIG. 30, the oil passage plate 490 is constructed integrally with the pump side plunger block 431 so that the rotary sliding surfaces 494 b and 444 face to each other, thereby forming one relative rotary sliding surface (matching surface 405 c). Accordingly, compared with the conventional construction that two relative rotary sliding surfaces are formed against the high pressure oil passage plate, the leak amount from the relative rotary sliding surface is reduced relatively. Therefore, the required amount of charge oil is suppressed, thereby reducing the power loss and the cost.

According to the above construction, as shown in FIG. 24, the high pressure oil passage plate, which is necessary in the conventional construction, is not provided, whereby the mass of the whole HST 401 can be reduced and the cost can be reduced.

According to the above construction, as shown in FIG. 24, the rear end surface of the rotary shaft 470 a and the front end surface of the rotary shaft 480 a are arranged oppositely closely. Accordingly, compared with the conventional construction that a bearing is disposed in the high pressure oil passage plate so as to pivotally support the rotary shaft, the total length of the HST 401 can be made more compact.

According to the above construction, as shown in FIG. 24, by providing the oil passage plate 490, sliding resistance generated between the rotary sliding surfaces 434 and 444 can be reduced with easy construction. Therefore, the power loss can be reduced.

According to the above construction, as shown in FIG. 24, the oil passage plate 490 is inserted into the bearing 497 so as to be rotatable relatively against the pump side plunger block 431, the motor side plunger block 441 and the rotary shafts 470 a and 480 a. Accordingly, even if a large gap is generated between the rotation speeds of the rotary shafts 470 a and 480 a, the oil passage plate 490 can be rotated freely and the rotations of the plunger blocks 431 and 441 are not restricted by the oil passage plate 490, thereby minimizing sliding resistance generated between the oil passage plate 490 and the plunger blocks 431 and 441.

According to the above construction, the separation element can be constructed by the simple construction, such as the eccentric arrangement of the rotary shafts 470 a and 480 a, whereby the part number of the hydrostatic stepless transmission can be reduced.

As shown in FIGS. 11 to 13 and 24, the charge oil supply mechanism and the check and relief mechanism of the HST 401 are constructed the same as the above-mentioned first embodiment. The HST 401 is also applicable to the above-mentioned second or third embodiment.

Next, explanation will be given on the construction of the case housing of the HST 401 constructed as the above.

As shown in FIG. 24, the case housing is divided into front and rear, and a half bearing guide 421 of the movable swash plate 433M, a bearing hole 422 for the bearing 430 b of the rotary shaft 470 a as an input shaft and a bearing hole 420 a of the bearing 497 for the oil passage plate 490 are formed integrally with the case housing 402 a at the side of the hydraulic pump 430. On the other hand, a bearing hole 424 for the rotary shaft 480 a as an input shaft is formed integrally with the case housing 402 b at the side of the hydraulic motor 440.

According to this construction, the mechanical processing can be reduced by molding the case housing by die casting, thereby reducing the cost.

In the above-mentioned construction, the hydraulic pump 430 is variable delivery type and the hydraulic motor 440 is fixed delivery type. However, the embodiment also can be applied to the opposite construction, that is, the construction that the hydraulic pump 430 is fixed delivery type and the hydraulic motor 440 is variable delivery type.

In the above-mentioned construction, the oil passage plate 490 is disposed in the pump side plunger block 431. However, the embodiment also can be applied to the opposite construction, that is, the construction that the oil passage plate 490 is disposed in the motor side plunger block 441.

In the above-mentioned construction, the charge oil supply mechanism and the check and relief mechanism are provided at the side of the hydraulic motor 440. However, the embodiment also can be applied to the opposite construction, that is, the construction that the charge oil supply mechanism and the check and relief mechanism are provided at the side of the hydraulic pump 430.

With regard to the construction (not shown) that the hydraulic pump 430 is constructed to be fixed displacement type, the hydraulic motor 440 is constructed to be variable displacement type, the charge oil supply mechanism and the check and relief mechanism are provided in the hydraulic pump 430, and the hydraulic motor 440 is provided at the side of the hydraulic motor 440, the case housing is divided into front and rear, and the bearing hole 422 for the rotary shaft 470 a as an input shaft is formed integrally with the case housing 402 a at the side of the hydraulic pump 430. On the other hand, the half bearing guide 421 of the movable swash plate 433M and the bearing hole 424 for the bearing 440 b of the rotary shaft 480 a as an input shaft is formed integrally with the case housing 402 b at the side of the hydraulic motor 440.

Accordingly, in addition to the above-mentioned embodiment, the mechanical processing can also be reduced by molding the case housing by die casting in the construction that that the hydraulic pump 430 is constructed to be fixed displacement type and the hydraulic motor 440 is constructed to be variable displacement type, thereby reducing the cost.

In addition, either of the constructions of the case housing shown in FIG. 16 (a) to (c) may be applied.

INDUSTRIAL APPLICABILITY

The present invention is available instead of the conventional hydrostatic stepless transmission, and is especially suitable for a part in which the space is required to be saved. Since the power loss is saved, the invention is suitable for a part in which high transmission efficiency is required. 

1. A hydrostatic stepless transmission comprising axial piston type hydraulic pump and hydraulic motor, constructed that a pump side plunger block faces to a motor side plunger block through their rotary sliding surfaces, a plurality of communication passages are formed which communicate cylinders formed in the plunger blocks with each other fluidally, a separation element is interposed in the communication passages, and in each of the pump and motor side plunger blocks, the separation element divides the communication passages into that of a suction area and that of a discharge area, characterized in that: the separation element is constructed in each of the plunger blocks by spool valves of the same number as the cylinders of the plunger block, the spool valves are arranged slidably radially centering on a rotary shaft of the plunger block, outer ends of the spool valves touch an inner peripheral surface of an inner ring of a bearing arranged eccentrically against the rotary shaft, the spool valves are slid following rotation of the plunger block along radial direction of the rotary shaft so as to open and close the oil passages communicating the cylinders of the plunger blocks with each other, and by closing the oil passages by the spool valves, each of the plunger blocks is divided into the suction area or the discharge area.
 2. The hydrostatic stepless transmission as set forth in claim 1, wherein the rotary shaft of the pump side plunger block and the rotary shaft of the motor side plunger block are disposed coaxially, and the rotary shaft and a planetary gear are combined so as to construct an input separation type hydro mechanical stepless transmission.
 3. The hydrostatic stepless transmission as set forth in claim 1, wherein the rotary shaft of the pump side plunger block and the rotary shaft of the motor side plunger block are disposed coaxially, and the rotary shaft and a planetary gear are combined so as to construct an output separation type hydro mechanical stepless transmission.
 4. The hydrostatic stepless transmission as set forth in claim 1, wherein the inner peripheral surface of the inner ring of the bearing is slanted against the axis of the rotary shaft.
 5. The hydrostatic stepless transmission as set forth in claim 1, wherein the sliding direction of the spool valves is slanted against the axis of the rotary shaft.
 6. The hydrostatic stepless transmission as set forth in claim 1, wherein a charge oil supply mechanism is disposed between a connection point to the charge pump provided in a case housing of the hydrostatic stepless transmission and the hydraulic circuit in the motor or pump side plunger block.
 7. The hydrostatic stepless transmission as set forth in claim 1, wherein a check mechanism is disposed between a connection point to the charge pump provided in a case housing of the hydrostatic stepless transmission and the hydraulic circuit in the motor or pump side plunger block.
 8. The hydrostatic stepless transmission as set forth in claim 1, wherein a case housing of the hydrostatic stepless transmission is divided near the separation element.
 9. The hydrostatic stepless transmission as set forth in claim 1, wherein a case housing of the hydrostatic stepless transmission is divided, the hydraulic motor and hydraulic pump are housed in a first housing, and an opening of the first housing is closed by the other housing.
 10. A hydrostatic stepless transmission comprising axial piston type hydraulic pump and hydraulic motor constructed that a pump side plunger block faces to a motor side plunger block through their rotary sliding surfaces, a plurality of communication passages are formed which communicate cylinders formed in the plunger blocks with each other fluidally, a separation element is interposed in the communication passages, and in each of the pump and motor side plunger blocks, the separation element divides the communication passages into that of a suction area and that of a discharge area, wherein the separation element is constructed that the rotary shafts arranged eccentrically support respectively the pump side plunger block and the motor side plunger block, a pump side port and a motor side port respectively communicated with the cylinders formed in the plunger blocks are formed so as to face to a relative rotary sliding surface between the plunger blocks, an oil passage is formed which communicates the ports of the plunger blocks, which are shifted by the eccentric arrangement, with each other by overlapping the ports of the plunger blocks with each other, the oil passage is closed by not overlapping the ports of the plunger blocks with each other on an extension of a line connecting the axes of the rotary shafts, and the closed oil passage of the oil passages divides the oil passages of each of the plunger blocks into that of the suction area and that of the discharge area.
 11. The hydrostatic stepless transmission as set forth in claim 10, wherein an oil passage plate rotated integrally with one of the plunger blocks is provided, and the oil passage plate touches the other plunger block slidably rotatively relatively so as to demarcate the relative rotary sliding surface between the plunger blocks, a plurality of oil passages are penetratively formed axially in the oil passage plate, an arrangement of the oil passages is substantially the same as that of the ports of the rotary sliding surface of the plunger block rotated integrally with the oil passage plate, and the rotary shaft of the plunger block rotated integrally with the oil passage plate is supported by the oil passage plate.
 12. The hydrostatic stepless transmission as set forth in claim 10, wherein a charge oil supply mechanism is disposed between a connection point to the charge pump provided in a case housing of the hydrostatic stepless transmission and the hydraulic circuit in the motor or pump side plunger block.
 13. The hydrostatic stepless transmission as set forth in claim 10, wherein a check mechanism is disposed between a connection point to the charge pump provided in a case housing of the hydrostatic stepless transmission and the hydraulic circuit in the motor or pump side plunger block.
 14. The hydrostatic stepless transmission as set forth in claim 10, wherein a case housing of the hydrostatic stepless transmission is divided near the separation element.
 15. The hydrostatic stepless transmission as set forth in claim 10, wherein a case housing of the hydrostatic stepless transmission is divided, the hydraulic motor and hydraulic pump are housed in a first housing, and an opening of the first housing is closed by the other housing. 